I've not heard of a single place around Palmetto/Bradenton area but there's a group that go riding down in Bonita Springs I believe. I have yet to make it down there though. gulfcoastjeepers.com is their site

Yep come check us out on Gulfcoastjeepers.com I am originally from bradenton but moved to ft myers.. bonita is about an hour and a half ride for you. maybe longer depending how far away you are from the interstate. There is one place I used to go off SR70 in bradenton but It wasnt anything too exciting and last I heard it was shut down.